Apparatus and method for detecting wobble signal read from optical disc

ABSTRACT

An apparatus and method for detecting a wobble signal read from an optical disc. The wobble signal detection apparatus comprises an analog/digital (A/D) converter for A/D-converting an analog wobble signal, read from the optical disc and then band pass filtered, a slope detector for detecting a slope of the A/D-converted wobble signal according to a variation thereof, and a wobble signal detector for detecting a peak point of the A/D-converted wobble signal using the detected wobble signal slope, and detecting/outputting a square-wave wobble signal with a high level or low level transition at the detected peak point. The slope detector calculates variations of data values of the A/D-converted wobble signal sampled within a predetermined period on the basis of predetermined different weights, accumulates the calculated values and detects the slope of the A/D-converted wobble signal on the basis of the accumulated value. The predetermined period is an interval where at least two wobble signal data samples are obtained. Therefore, a stable wobble signal can be detected even though a low-frequency fluctuation component and DC offset component are introduced into the analog wobble signal read from the optical disc or the analog wobble signal varies in amplitude.

This application is a Continuation of application Ser. No. 10/294,818,filed on Nov. 15, 2002 now U.S. Pat. No. 6,809,997, and for whichpriority is claimed under 35 U.S.C. § 120; and this application claimspriority of Application Nos. 2001-0071611 filed in Korea on Nov. 17,2001, and 2001-0079074 filed in Korea on Dec. 13, 2001, under 35 U.S.C.§ 119; the entire contents of all are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for detecting awobble signal read from an optical disc such as a writable compact disc(CD) or digital versatile disc (DVD).

2. Description of the Related Art

It is common that a writable optical disc, such as a digital versatiledisc-random access memory (DVD-RAM) or digital versatiledisc-re-writable (DVD-RW), has grooves formed along spiral or concentrictracks. Here, portions of the optical disc other than the grooves aretypically called lands. Data can be recorded on only any one or both ofeach groove and each land according to a writing method. A specificvariation is applied to a wall of each groove in a groove formationprocess, and a specific frequency signal is generated based on thespecific variation in a recording/reproduction process, so it can beused as auxiliary clock means. Here, the specific variation is called awobble and the specific frequency signal is called a wobble signal.

FIG. 1 shows the construction of a conventional apparatus for detectinga wobble signal read from an optical disc. As shown in this drawing, theconventional wobble signal detection apparatus comprises a band passfilter (BPF) 10 for filtering a push-pull signal, or an analog wobblesignal, read from a writable optical disc, for example, a DVD-RW at apredetermined frequency band to remove a high-frequency noise component,a direct current (DC) offset component, etc. therefrom. Ananalog/digital (A/D) converter (ADC) 11 is provided to A/D-convert anoutput analog wobble signal of the predetermined frequency band from theband pass filter 10 to output a digital wobble signal. A wobble signaldetector 12 acts to slice the A/D-converted digital wobble signal on thebasis of a predetermined reference level, for example, a zero level todetect/output a square-wave wobble signal. A wobble phase locked loop(PLL) 100 is provided to output a wobble PLL clock synchronized with thesquare-wave wobble signal. FIG. 2 shows measured waveforms of thefiltered wobble signal from the band pass filter 10, the sliced wobblesignal from the wobble signal detector 12 and the PLL clock from thewobble phase locked loop 100.

The conventional wobble signal detection apparatus further comprises abit detector 16 for detecting/converting the square-wave wobble signalinto a stream of bits having values of 1 or 0, using the wobble PLLclock. A synchronous (Sync) detector 17 acts to detect a synchronouspattern placed in the square-wave wobble signal from the bit stream andgenerate and output a synchronous signal corresponding to the detectedsynchronous pattern. An address decoder 18 is provided to decode aphysical address of the optical disc from the bit stream on the basis ofthe synchronous signal.

The wobble PLL 100 includes a phase error detector 13 for detecting aphase error at a point of time that the A/D-converted wobble signalcrosses a zero point from positive to negative, namely, a negative zerocrossing point (referred to hereinafter as ‘NZCP’) as shown in FIG. 3. Atime count value that determines an oscillating frequency of a digitalcontrolled oscillator (DCO) 15 in the wobble PLL 100, for example, afree down time count value, is always corrected with the phase errordetected at the NZCP.

At this time, in a case (lead case) where the phase of the PLL clock,which is generated by the digital controlled oscillator 15, is ahead ofthat of the A/D-converted wobble signal, the phase error detector 13detects/generates a positive phase error as shown in FIG. 3 and outputsthe generated phase error to a loop filter 14 in the wobble PLL 100. Theloop filter 14 then corrects a time count value for determination of aclock frequency of the digital controlled oscillator 15 into a smallervalue according to the positive phase error.

On the other hand, in a case (lag case) where the phase of the PLL clockgenerated by the digital controlled oscillator 15 is behind that of theA/D-converted wobble signal, the phase error detector 13detects/generates a negative phase error as shown in FIG. 3 and outputsthe generated phase error to the loop filter 14, which then corrects thetime count for determination of the clock frequency of the digitalcontrolled oscillator 15 into a larger value according to the negativephase error.

As a result, the wobble PLL 100 continuously performs a phase errorcorrection operation for synchronization of the PLL clock with thewobble signal by detecting a phase error at the NZCP and correcting thetime count for determination of the clock frequency of the digitalcontrolled oscillator 15 on the basis of the detected phase error.

However, recently, as the optical disc becomes higher in recordingdensity, recording tracks thereof have denser pitches, resulting in agreater crosstalk effect caused by a wobble signal of an adjacent track.This greater crosstalk effect makes the output wobble signal from theband pass filter 10 very small in signal to noise (S/N) ratio, so astable wobble signal cannot be detected by the conventional wobblesignal detection apparatus.

In addition, provided that a tracking servo and focusing servo areunstable or a surface vibration of the optical disc, etc. occur, alow-frequency fluctuation component and DC offset component will beintroduced into the output wobble signal from the band pass filter 10 orthe wobble signal will vary in amplitude. For example, as shown in FIG.4, in the case {circle around (1)} where a stable wobble signal with aconstant amplitude is outputted from the band pass filter 10, a stablewobble signal {circle around (4)} is normally detected by the wobblesignal detector 12. Alternatively, in the case {circle around (2)} wherea low-frequency fluctuation component and DC offset component arecontained in the output wobble signal from the band pass filter 10, orin the case {circle around (3)} where the output wobble signal from theband pass filter 10 has a varying amplitude and DC offset component, anabnormal wobble signal {circle around (5)} or {circle around (6)} isdetected by the wobble signal detector 12. Consequently, the wobblephase locked loop cannot normally perform the phase error correctionoperation.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide anapparatus and method for detecting a stable wobble signal even though alow-frequency fluctuation component and DC offset component areintroduced into an analog wobble signal read from an optical disc or theanalog wobble signal varies in amplitude.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a wobble signaldetection apparatus comprising analog/digital (A/D) conversion means forA/D-converting an analog wobble signal, read from an optical disc andthen band pass filtered; slope detection means for detecting a slope ofthe A/D-converted wobble signal according to a variation thereof; andwobble signal detection means for detecting a peak point of theA/D-converted wobble signal using the detected wobble signal slope, anddetecting/outputting a square-wave wobble signal with a high level orlow level transition at the detected peak point; the slope detectionmeans calculating variations of data values of the A/D-converted wobblesignal sampled within a predetermined period on the basis ofpredetermined different weights, accumulating the calculated values anddetecting the slope of the A/D-converted wobble signal on the basis ofthe accumulated value, the predetermined period being an interval whereat least two wobble signal data samples are obtained.

In accordance with another aspect of the present invention, there isprovided a wobble signal detection method comprising the steps of a)band pass filtering and A/D-converting an analog wobble signal read froman optical disc, and detecting a slope of the A/D-converted wobblesignal; b) detecting a peak point of the A/D-converted wobble signalusing the detected wobble signal slope; and c) detecting/outputting asquare-wave wobble signal with a high level or low level transition atthe detected peak point; the step a) of detecting the wobble signalslope including the step of comparing data values of the A/D-convertedwobble signal sampled within a predetermined period with an arbitraryreference wobble signal data value, respectively, obtaining therespective differences as a result of the comparisons, multiplying theobtained differences by different weights, respectively, accumulatingthe multiplied values, comparing the accumulated value with apredetermined threshold value, and detecting the wobble signal slope inaccordance with the compared result.

In accordance with a further aspect of the present invention, there isprovided a wobble signal detection method comprising the steps of a)band pass filtering an analog wobble signal read from an optical disc,and A/D-converting the filtered wobble signal into a digital wobblesignal; b) detecting a peak point of the A/D-converted digital wobblesignal; c) determining whether a counted value obtained byfrequency-counting an interval between the detected wobble signal peakpoint and a just previously detected wobble signal peak pointcorresponds to a bit length of an integer multiple of 3; and d)initializing the counted value if it corresponds to the bit length ofthe integer multiple of 3, performing a re-counting operation, anddetecting/outputting a square-wave wobble signal with a high level orlow level transition at a point of time that a re-counted valuecorresponds to a desired bit length.

In accordance with yet another aspect of the present invention, there isprovided a wobble signal detection apparatus comprising A/D conversionmeans for A/D-converting an analog wobble signal, read from an opticaldisc and then band pass filtered; slope detection means for detecting aslope of the A/D-converted wobble signal according to a variationthereof; peak detection means for detecting a peak point of theA/D-converted wobble signal using the detected wobble signal slope;counting means for frequency-counting an interval between the detectedwobble signal peak point and a just previously detected wobble signalpeak point; and level transition means for, if a counted value obtainedby frequency-counting the interval between the detected wobble signalpeak point and the just previously detected wobble signal peak pointcorresponds to a bit length of an integer multiple of 3, initializingthe counted value, and making a high level or low level transition at apoint of time that a re-counted value corresponds to a desired bitlength.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram showing the construction of a conventionalapparatus for detecting a wobble signal read from an optical disc;

FIG. 2 is a waveform diagram of signals detected by the conventionalapparatus of FIG. 1;

FIG. 3 is a waveform diagram of a phase error, PLL clock and digitalcontrolled oscillator time count in a wobble PLL in FIG. 1;

FIG. 4 is a waveform diagram of wobble signals abnormally detected by awobble signal detector in FIG. 1;

FIG. 5 is a block diagram showing the construction of an apparatus fordetecting a wobble signal read from an optical disc in accordance with apreferred embodiment of the present invention;

FIG. 6 is a waveform diagram illustrating a wobble signal slopedetection process in accordance with the embodiment of the presentinvention;

FIG. 7 is a waveform diagram of wobble signal slope detection signals inaccordance with the embodiment of the present invention;

FIG. 8 is a waveform diagram illustrating a wobble signal peak detectionprocess in accordance with the embodiment of the present invention;

FIG. 9 is a waveform diagram of a wobble signal peak detection signal inaccordance with the embodiment of the present invention;

FIG. 10 is a waveform diagram of wobble signals normally detected by thewobble signal detection apparatus and method in accordance with theembodiment of the present invention;

FIG. 11 is a waveform diagram illustrating a state where ahigh-frequency noise component is contained in a wobble signal inputtedto a slope detector in accordance with the embodiment of the presentinvention;

FIG. 12 is a waveform diagram illustrating a different example of thewobble signal slope detection process in accordance with the embodimentof the present invention;

FIG. 13 is a waveform diagram of wobble signal slope detection signalsgenerated according to the example of FIG. 12;

FIG. 14 is a block diagram showing the construction of an apparatus fordetecting a wobble signal read from an optical disc in accordance withan alternative embodiment of the present invention;

FIG. 15 is a detailed block diagram of a wobble signal detector in FIG.14;

FIG. 16 is a waveform diagram of wobble signals detected by the wobblesignal detection apparatus in accordance with the second embodiment ofthe present invention;

FIG. 17 is a flow chart illustrating a wobble signal detection method inaccordance with the second embodiment of the present invention;

FIG. 18 is a waveform diagram illustrating a process of detecting awobble signal with a level transition in the wobble signal detectionmethod in accordance with the second embodiment of the presentinvention; and

FIG. 19 is a waveform diagram illustrating the comparison between awobble signal detected by the wobble signal detection method inaccordance with the second embodiment of the present invention andwobble signals abnormally detected by conventional wobble signaldetection methods.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 5, there is shown in block form the constructionof an apparatus for detecting a wobble signal read from an optical discin accordance with a preferred embodiment of the present invention.

As shown in FIG. 5, the wobble signal detection apparatus comprises aslope detector 21 for detecting a positive slope and negative slope of awobble signal, A/D-converted as stated previously with reference to FIG.1, and a wobble signal detector 22 for detecting/deciding a peak pointof the A/D-converted wobble signal on the basis of the positive slopeand negative slope and detecting/outputting a square-wave wobble signalwith a high level or low level transition at the decided peak point.

The wobble signal detection apparatus further comprises a wobble PLL 200including a phase error detector 23, loop filter 24 and digitalcontrolled oscillator 25. The phase error detector 23compares/calculates a phase error between an output PLL clock from thedigital controlled oscillator 25 and the square-wave wobble signal withthe level transition at the peak point. The loop filter 24 filters anoutput phase error value from the phase error detector 23 to generate aphase correction value. The digital controlled oscillator 25 corrects acurrent PLL clock oscillating frequency according to the phasecorrection value generated by the loop filter 24 to output the PLLclock.

The PLL clock generated and outputted by the wobble PLL 200 is alsoapplied to the bit detector 16 to which the A/D-converted wobble signalis inputted. The bit detector 16 detects/converts the A/D-convertedwobble signal into a stream of bits having values of 1 or 0, using thePLL clock. The synchronous detector 17 detects a synchronous patternplaced in the A/D-converted wobble signal from the bit stream andgenerates and outputs a synchronous signal corresponding to the detectedsynchronous pattern. The address decoder 18 decodes a physical addressof the optical disc from the bit stream from the bit detector 16 on thebasis of the synchronous signal from the synchronous detector 17.

A detailed description will hereinafter be given of the wobble signaldetection operation performed by the slope detector 21 and wobble signaldetector 22.

FIG. 6 is a waveform diagram illustrating a wobble signal slopedetection process in accordance with the embodiment of the presentinvention, and FIG. 7 is a waveform diagram of wobble signal slopedetection signals in accordance with the embodiment of the presentinvention. As shown in FIG. 6, an output analog wobble signal from theband pass filter 10 is A/D-converted by the A/D converter 11 and theninputted to the slope detector 21. In order to remove a high-frequencynoise component mixed in the A/D-converted wobble signal, the slopedetector 21 compares a value of the currently A/D-converted digitalwobble signal data with that of digital wobble signal data A/D-convertedbefore a predetermined period of time (for example, 10% of a wobblesignal period), not the just previously A/D-converted digital wobblesignal data, to obtain a difference between the two values. The slopedetector 21 then detects a slope of the wobble signal if the obtaineddifference is greater than or equal to a predetermined threshold value,for example, 2 bits. For example, assume that 70 wobble signal datasamples are obtained during one wobble signal period, as shown in FIG.6. In this case, if the currently A/D-converted digital wobble signaldata is ‘1101 10XX’ (XX are ignored) and digital wobble signal datasampled before 10% of the wobble signal period, namely, wobble signaldata sampled before 7 samples is ‘1111 01XX’ (XX are ignored), thecompared result (1101 10XX−1111 01XX) is a negative (−) value indicativeof a difference of 2 or more bits. As a result, the slope detector 21detects a negative slope of the wobble signal. To the contrary, in thecase where the compared result is a positive (+) value indicative of adifference of 2 or more bits, the slope detector 21 detects a positiveslope of the wobble signal. Accordingly, the slope detector 21detects/outputs, as shown in FIG. 6, a negative slope detection signalwhich becomes high in level when the compared result is a negative (−)value, and a positive slope detection signal which becomes high in levelwhen the compared result is a positive (+) value, respectively.

Hence, the positive slope detection signal and the negative slopedetection signal inputted to the wobble signal detector 22 havedifferent waveforms as shown in FIG. 7.

FIG. 8 is a waveform diagram illustrating a wobble signal peak detectionprocess in accordance with the embodiment of the present invention, andFIG. 9 is a waveform diagram of a wobble signal peak detection signal inaccordance with the embodiment of the present invention.

Upon receiving the positive slope detection signal and negative slopedetection signal as stated above, the wobble signal detector 22 createsa virtual window having a certain length, and accumulates positive slopevalues and negative slope values existing within the created window,respectively. The length of the window is preferably set to ½ (T/2) ofone wobble signal period (1T).

Then, the wobble signal detector 22 compares the accumulated positiveslope value and the accumulated negative slope value with each other,and outputs a high signal if the accumulated positive slope value isgreater than the accumulated negative slope value and a low signal ifthe accumulated positive slope value is not greater than the accumulatednegative slope value.

As a result, the wobble signal detector 22 detects/decides a peak pointof the analog wobble signal in response to the positive slope detectionsignal and negative slope detection signal and outputs a square-wavewobble signal with a high level or low level transition at the decidedpeak point. The analog wobble signal, the positive slope, the negativeslope, and the wobble signal outputted from the wobble signal detectorhave waveforms as shown in FIG. 9, respectively.

Therefore, in accordance with the preferred embodiment of the presentinvention, as shown in FIG. 10, in the case {circle around (1)}′ where astable wobble signal with a constant amplitude is outputted from theband pass filter, a stable wobble signal {circle around (2)}′ with alevel transition at a peak point of the output wobble signal from theband pass filter is normally detected by the wobble signal detector 22.Further, even in the case {circle around (3)}′ where a low-frequencyfluctuation component and DC offset component are contained in theoutput wobble signal from the band pass filter, or in the case {circlearound (5)}′ where the output wobble signal from the band pass filterhas a varying amplitude and DC offset component, a stable wobble signal{circle around (4)}′ or {circle around (6)}′ with a level transition ata peak point of the output wobble signal from the band pass filter isdetected/outputted by the wobble signal detector 22.

On the other hand, in the case where a notch-shaped or spark-shapedhigh-frequency noise component is contained in the filtered analogwobble signal from the band pass filter 10, a slope detection error ofthe wobble signal may occur due to the high-frequency noise component. Aslope detection method for preventing such a slope detection error willhereinafter be described in detail with reference to the annexeddrawings.

As shown in FIG. 11, in the case where a high-frequency noise componentis introduced into an analog wobble signal (indicated by a dotted line),it is filtered by the band pass filter 10 and then inputted as a wobblesignal (indicated by a solid line) with a notch-shaped or spark-shapedhigh-frequency noise component to the A/D converter 11.

As a result, wobble signal data sampled and A/D-converted by the A/Dconverter 11 has values irregularly incremented and decremented due tothe notch-shaped or spark-shaped noise component. For example, as shownin FIG. 11, in a case (good sampling case) where wobble signal datavalues obtained by sampling the wobble signal with the high-frequencynoise component are X(0)˜X(n), wobble signal data corresponding to theoriginal wobble signal is normally outputted to the slope detector 21.However, in a case (bad sampling case) where wobble signal data valuesobtained by sampling the wobble signal with the notch-shaped orspark-shaped high-frequency noise component are X′ (0)˜X′ (n), wobblesignal data different from the original wobble signal is outputted tothe slope detector 21.

In other words, as shown in an interval ‘A’ in FIG. 11, the (n+2)thsampled wobble signal data value X′ (1) is larger than the (n+3)thsampled wobble signal data value X′ (2). As a result, when a slope isdetermined on the basis of the comparison between the wobble signal datavalues at the two points, the slope is erroneously detected as a slopewhere the wobble signal decreases, although the original wobble signalincreases.

Therefore, the slope detector 21, as shown in FIG. 12, creates a windowhaving a certain interval, for example, an interval where 11 wobblesignal data values X(0)˜X(10) are sampled, sets the first wobble signaldata value X(0) sampled within the created window as a reference wobblesignal data value, compares the set reference wobble signal data valuewith each of the subsequent wobble signal data values X(1)˜X(10)sequentially sampled within the window, obtains the respectivedifferences as a result of the comparisons, and multiplies the obtaineddifferences by different weights W(1)˜W(10), respectively.

Then, the slope detector 21 accumulates all values obtained bymultiplying the differences, respectively, by the different weightsW(1)˜W(10), compares the accumulated value with a predetermined positivethreshold value for positive slope detection and a predeterminednegative threshold value for negative slope detection, respectively, anddetects/outputs a positive slope and negative slope of the wobble signalwithin the window in accordance with the compared results.

The weights W(1)˜W(10) are preferably preset to values (W(1)<W(2) . . .W(9)<W(10)) which increase in proportion to time differences or spaceddistances between the reference wobble signal data value X(0) firstsampled within the window and the subsequent wobble signal data valuesX(1)˜X(10) sequentially sampled within the window.

If a wobble signal slope is detected within a given window Window 1,then the above wobble signal slope detection process shifts to a nextwindow Window 2, as shown in FIG. 12.

Accordingly, the slope detector 21 repeats a sequence of operations ofsetting the first wobble signal data value X(1) sampled within theshifted window Window 2 as a reference wobble signal data value,comparing the set reference wobble signal data value with each of thesubsequent wobble signal data values X(2)˜X(11) sequentially sampledwithin the shifted window, obtaining the respective differences as aresult of the comparisons, and multiplying the obtained differences bydifferent weights, respectively, as expressed by the following equation:

$\begin{matrix}{{{Sp}(k)} = \begin{matrix}{\sum\limits_{i = 1}^{N}\{ {\lbrack {{{x(i)} - {X(0)}} > 0} \rbrack?} } &  \mspace{20mu}{{w(i)}\text{:}0} \}\end{matrix}} \\{{{Sn}(k)} = \begin{matrix}{\sum\limits_{i = 1}^{N}\{ {\lbrack {{{x(i)} - {X(0)}} > 0} \rbrack?} } &  {{- {w(i)}}\text{:}0} \}\end{matrix}} \\{{y(k)} = {{{Sp}(k)} + {{Sn}(k)}}}\end{matrix}\quad$ $\begin{matrix}\begin{matrix}{{if}\mspace{14mu}{( {{y(k)} < {Nth}} )?}} \\{{else}\mspace{14mu}{if}\mspace{14mu}{( {{Nth} < {y(k)} < {Pth}} )?}} \\{{else}\mspace{14mu}{if}\mspace{14mu}{( {{Pth} < {y(k)}} )?}}\end{matrix} & \begin{matrix}{{{Slope}(k)} = {Negative}} \\{{{Slope}(k)} = {Zero}} \\{{{Slope}(k)} = {Positive}}\end{matrix}\end{matrix}\quad$

Here, N is the size of data to be accumulated, X(n) is sampled data,X(0) is sampled reference data, W(n) is a weight to a slope based on twosampled data, Sp(k) is a value obtained by accumulating positive slopeweights of respective sampled data on the basis of X(0), Sn(k) is avalue obtained by accumulating negative slope weights of the respectivesampled data on the basis of X(0), Pth is a positive threshold value,Nth is a negative threshold value, and Slope(n) is a slope at X(0).

Hence, the positive slope detection signal and negative slope detectionsignal detected/outputted by the above-described equation and operationhave stable waveforms with no high-frequency noise component as shown inFIG. 13, so the wobble signal detector 22 can detect a peak point moreaccurately in the wobble signal peak detection process previously statedwith reference to FIG. 8. Therefore, even in the case where thenotch-shaped or spark-shaped high-frequency noise component is containedin the analog wobble signal, a slope detection error of the wobblesignal due to the high-frequency noise component can be prevented fromoccurring.

The present embodiment has been disclosed for illustrative purposes, andthe slope detector 21, wobble signal detector 22 and phase errordetector 23 may be integrated to configure a single unit.

FIG. 14 shows the construction of an apparatus for detecting a wobblesignal read from an optical disc in accordance with an alternativeembodiment of the present invention. In this drawing, the same parts asthose in FIG. 1 are denoted by the same reference numerals and adetailed description thereof will hereinafter be omitted.

A wobble signal detector 30 in the second embodiment includes, as shownin FIG. 15, a slope detector 31, peak detector 32, level transitioncorrector 33 and frequency counter 34.

The slope detector 31 detects a slope of a digital wobble signalA/D-converted by the A/D converter 11. The peak detector 32 detects apeak point of the digital wobble signal using the detected wobble signalslope. The frequency counter 34 frequency-counts an interval between thepeak point detected by the peak detector 32 and the just previouslydetected peak point and outputs the counted value to the leveltransition corrector 33. If the counted value is a bit length which isan integer multiple of 2, for example, a 2T or 4T length defined in awritable optical disc such as a DVD-RW, the level transition corrector33 makes a high or low level transition based on the wobble signal slopeat the peak point detected by the peak detector 32. In the case wherethe counted value is a bit length which is an integer multiple of 3, forexample, a 3T length, the level transition corrector 33 resets thecounted value to resume the counting operation of the frequency counter34, and then makes a high or low level transition at a point of timethat the re-counted value becomes a 1T length.

Therefore, even though the A/D-converted digital wobble signal containsa low-frequency fluctuation component, a DC offset component and anamplitude variation, the wobble signal detector 30 can detect a stablewobble signal. In particular, the wobble signal detector 30 candetect/output a square-wave wobble signal with a bit length of aninteger multiple of 2 which is capable of making the address decodingeasier.

For example, as shown in FIG. 16, in the case {circle around (1)} wherethe digital wobble signal inputted to the wobble signal detector 30 is astable wobble signal with a constant amplitude, the peak detector 32 inthe wobble signal detector 30 detects a peak point of the digital wobblesignal according to a slope variation thereof and normally detects astable square-wave wobble signal {circle around (7)} on the basis of thedetected peak point. Further, even in the case {circle around (2)} wherea low-frequency fluctuation component and DC offset component arecontained in the digital wobble signal, or in the case {circle around(3)} where the digital wobble signal has a varying amplitude, the peakdetector 32 normally detects a stable square-wave wobble signal {circlearound (8)} or {circle around (9)} on the basis of a peak point of thedigital wobble signal.

On the other hand, the level transition corrector 33 receives thesquare-wave wobble signal detected/outputted from the peak detector 32and outputs a square-wave wobble signal with a pulse width of a bitlength of an integer multiple of 2, as will hereinafter be described indetail.

FIG. 17 is a flow chart illustrating a method for detecting a wobblesignal read from an optical disc in accordance with the secondembodiment of the present invention.

First, the wobble signal detector 30 detects a slope of an outputdigital wobble signal from the A/D converter 11 (step S10) andcontinuously performs a peak detection operation of detecting a peakpoint of the digital wobble signal based on the detected slope. If apeak point of the wobble signal is detected (step S11), then the wobblesignal detector 30 checks a value frequency-counted beginning with thepreviously detected peak point (step S12).

For example, upon detecting a Kth peak point P_(K) by monitoring theslope of the digital wobble signal, the wobble signal detector 30 checksa value frequency-counted beginning with the previously detected (K−1)thpeak point P_(K−1).

In the case where the checked frequency-counted value is a bit length ofan integer multiple of 3, for example, a 3T length (step S13), thewobble signal detector 30 resets the counted value and then resumes thecounting operation (step S14). Thereafter, if the re-counted valuebecomes a 1T length (step S15), then the wobble signal detector 30 makesa high or low level transition at that time point.

In other words, in the case where a frequency count increasing from the(K−1)th peak point P_(K−1)to the Kth peak point P_(K)has a valuecorresponding to the 3T length, as shown in FIG. 18, the wobble signaldetector 30 generates no trigger point for a level transition,initializes the frequency count to zero, and then performs there-counting operation.

Thereafter, when the frequency re-count has a value corresponding to the1T length at the above step S15, the wobble signal detector 30 generatesa trigger point so as to make a high level transition of a 4T lengthcorresponding to an integer multiple of 2 (step S16). At this time, thewobble signal detector 30 makes a high level transition when the digitalwobble signal slope at the Kth peak point P_(K) changes from negative topositive. Alternatively, the wobble signal detector 30 makes a low leveltransition when the digital wobble signal slope at the Kth peak pointP_(K) changes from positive to negative.

On the other hand, in the case where the checked frequency-counted valueis a bit length of an integer multiple of 2, for example, a 2T or 4Tlength at the above step S13, the wobble signal detector 30 generates atrigger point for a level transition so as to make a high/low leveltransition (step S16). Thereafter, the wobble signal detector 30 resetsthe frequency-counted value to zero (step S17) and then repeats theabove operation according to whether the system is ended (step S18).

Therefore, the wobble signal detector 22 detect/outputs a square-wavewobble signal with a pulse width of a bit length of an integer multipleof 2, for example, the 2T or 4T length, thereby enabling the addressdecoder 18 to perform the address decoding operation in a simplermanner.

For example, as shown in FIG. 18, when a level transition is made on thebasis of a point of peak detection time, a wobble signal isdetected/outputted in the form of peak data with 2T, 3T and 4T lengths.In this case, the address decoding operation must be performed at alength of ½ T which is the greatest common factor of 2T, 3T and 4T,thereby making the address decoder 18 complicated in construction.However, the wobble signal detector 30 enables the address decoder 18 toperform the address decoding operation at a length of 2T which is thegreatest common factor of 2T and 4T, so the address decoder 18 canbecome simpler in construction.

As seen from FIG. 19, in the case where a digital wobble signalA/D-converted by the A/D converter 11 has a distorted pattern containinga low-frequency fluctuation component, an amplitude variation, etc., awobble signal (Slice Data Signal) detected/outputted by a conventionalslice detection method is an abnormal square-wave wobble signal whichhas a pulse width of a 2T or 4T length, but is discontinuouslyinterrupted due to the amplitude variation, etc. Also, a wobble signal(Peak Data Signal) detected/outputted by a conventional peak detectionmethod is a square-wave wobble signal which is stable regardless of theamplitude variation, etc., but has a pulse width of a 2T, 3T or 4Tlength, thereby complicating the address decoding operation.

On the other hand, a wobble signal (Corrected Transition Data Signal)detected/outputted by the peak detection & transition correction methodaccording to the second embodiment of the present invention is asquare-wave wobble signal which is stable irrespective of the amplitudevariation, etc. and has a pulse width of the 2T or 4T lengthfacilitating the address decoding operation.

As apparent from the above description, the present invention providesan apparatus and method for detecting a stable wobble signal even thougha low-frequency fluctuation component and DC offset component areintroduced into an analog wobble signal read from an optical disc or theanalog wobble signal varies in amplitude. Further, according to thepresent invention, an address decoder for decoding a physical address ofthe optical disc can be made simpler in construction.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An apparatus for detecting a wobble signal, comprising: a slopedetection unit configured to detect a slope of the wobble signalaccording to a variation thereof, the slope including a positive slopeand a negative slope; and a wobble signal detection unit configured todetect a peak point of said wobble signal using the detected wobblesignal slope, and to output a square-wave wobble signal with a highlevel or low level transition at the detected peak point, wherein saidslope detection unit detects the positive slope and the negative slopesuch that the positive slope of the wobble signal is detected if acompared value between a current wobble signal and a previous wobblesignal represents a positive slope value, and the negative slope of thewobble signal is detected if the compared value between the currentwobble signal and the previous wobble signal represents a negative slopevalue.
 2. The apparatus of claim 1, wherein the wobble signal detectionunit detects the peak point based on the positive slope value and thenegative slope value present within a window time period.
 3. Theapparatus of claim 2, wherein the wobble signal detection unit detectsthe peak point with a high level or low level according to a differencebetween the positive slope value and the negative slope value.
 4. Theapparatus of claim 3, wherein the wobble signal detection unit detectsthe peak point with the high level if the positive slope value is largerthan the negative slope value and the peak point with the low level ifthe positive slope value is smaller than the negative slope value. 5.The apparatus of claim 2, wherein the window time period has a halflength of one period of the wobble signal.
 6. A method of detecting awobble signal read from an optical disc, comprising: a) detecting apositive slope value and a negative slope value of the wobble signalread from the optical disc; b) detecting a peak point of the wobblesignal based on the detected positive and negative slope values; and c)outputting a square-wave wobble signal with a high level or a low leveltransition at the detected peak point as a result of step b).
 7. Themethod of claim 6, wherein said step a) detects the positive slope valueof the wobble signal if a compared value between a current wobble signaland a previous wobble signal represents the positive slope value, anddetects the negative slope of the wobble signal if the compared valuebetween the current wobble signal and the previous wobble signalrepresents the negative slope value.
 8. The method of claim 6, whereinthe step b) detects the peak point based on the positive slope value andthe negative slope value present within a window time period.
 9. Themethod of claim 8, wherein the step b) detects the peak point with thehigh level or the low level according to a difference between thepositive slope value and the negative slope value.
 10. The method ofclaim 9, wherein the step b) detects the peak point with the high levelif the positive slope value is larger than the negative slope value andthe peak point with the low level if the positive slope value is smallerthan the negative slope value.
 11. A method of detecting a wobblesignal, comprising: a) detecting a peak point of the wobble signal usinga slope of the wobble signal; b) comparing a period between a first peakpoint and a second peak point with a predetermined period; and c)determining a transition point as a result of step b), wherein thetransition point is to determine a transition to output a square-wavewobble signal with a high or a low level.
 12. The method of claim 11,wherein the step b) includes: b-1) determining whether a counted valueobtained by frequency-counting an interval between the first peak pointand the second peak point corresponds to a desired bit length.
 13. Themethod of claim 12, wherein the step b-1) includes: b-1-1) initializingthe counted value if the counted value does not correspond to thedesired bit length; and b-1-2) performing a re-counting operation, anddetermining whether the counted value corresponds to the desired bitlength.
 14. The method of claim 11, further comprising: d) outputtingthe square-wave wobble signal with the high level or the low level whenthe compared period corresponds to the desired bit length.
 15. Themethod of claim 11, wherein the step b) includes: b-1-1) resetting acounted value if the counted value obtained by frequency-counting aninterval between a currently detected peak point and a previouslydetected peak point corresponds to a 3nT length (n is an integer valueand T is a channel bit length); and performing a re-counting operationto obtain a re-counted value.
 16. The method of claim 15, wherein saidstep c) determines the high level or the low level at a point of timethat the re-counted value corresponds to a 1T length.
 17. The method ofclaim 11, wherein said step b) determines if a counted value obtained byfrequency-counting an interval between a currently detected peak pointand a previously detected peak point corresponds to 2nT length (n is aninteger value and T is a channel bit length).
 18. The method of claim17, wherein said step c) determines the high level or the low level at apoint of time that the counted value corresponds to the 2nT length.